Management of Gray Mold of Iceberg Lettuce by Biological Control Agents and Chitosan Formulations

Abstract

Gray mold caused by Botrytis is the major problem in iceberg lettuce cultivation in poly tunnels in Sri Lanka. Currently management of this disease of lettuce depends mainly on foliar application of fungicides. Continues application of fungicides for control of gray mold could not be recommended as lettuce mainly consume as fresh vegetables. Therefore, studies were conducted to identify the causal agent, varietal resistance to pathogen and effective chitosan formulation and biological control agents on control of gray mold diseases of ice berg lettuce in poly tunnels. Causal agent of this disease was identified as Botrytis cinerea. Commercially grown varieties Eden and Maruli were equally susceptible to the disease. Different isolates of pathogen were shown different virulence levels on iceberg lettuce variety Eden. In vitro test showed that, almost complete inhibition of mycelia growth of all Botrytis isolates at 600 ppm chitopower 2 and liquid formulation of Trichoderma asperellum (4x105 conidia/ml) but 600 ppm chitopower 1 or liquid formulation of fluorescent Pseudomonas (106 bacteria/ml) or fungicide-Dicloran 75WP (3000ppm) were suppressed some isolates only. Studies in poly tunnel showed that lowest disease severity index (3.6% DSI) of gray mold in iceberg lettuce plants treated with Trichoderma asperellum and highest DSI (77.7%) in control treatment. Dicloran 75WP, chitopower 2 and fluorescent Pseudomonas were recorded 16.6%, 18.5% and 46.2% DSI respectively. Results revealed that Trichoderma asperellum bio control agent and chitopower 2 could be used as alternatives to synthetic fungicides in controlling of gray mold disease of iceberg lettuce grown in poly tunnels.